1. Field of the Invention
The present invention is directed to intraocular implant devices and more specifically to shape memory capsular shaping devices for combining with a post-phacoemulsification capsular sac to provide a biomimetic complex that can mimic the energy-absorbing and energy-releasing characteristics of a natural young accommodative lens capsule. The shape memory capsular shaping devices can further be combined with an independent or integrated optics to provide an accommodating intraocular lens.
2. Description of the Related Art
The human lens capsule can be afflicted with several disorders that degrade its functioning in the vision system. The most common lens disorder is a cataract which consists of the opacification of the normally clear, natural crystalline lens matrix in a human eye. The opacification usually results from the aging process but can also be caused by heredity or diabetes. FIG. 1A illustrates a lens capsule comprising a capsular sac with an opacified crystalline lens nucleus. In a typical cataract procedure as performed today, the patient's opaque crystalline lens is replaced with a clear lens implant or IOL. (See FIGS. 1A and 1B.) The vast majority of cataract patients must wear prescription eyeglasses following surgery to see properly. The IOLs in use today provide the eye with a fixed focal length, wherein focusing on both close-up objects and distant objects is not possible. Intraocular lens implantation for cataracts is the most commonly performed surgical procedure in elderly patients in the U.S. Nearly three million cataract surgeries are performed each year in the U.S., with an additional 2.5 million surgeries in Europe and Asia.
Mechanisms of Accommodation.
Referring to FIG. 1A, the human eye defines an anterior chamber 10 between the cornea 12 and iris 14 and a posterior chamber 20 between the iris and the lens capsule 102. The vitreous chamber 30 lies behind the lens capsule. The lens capsule 102 that contains the crystalline lens matrix LM or nucleus has an equator that is attached to cobweb-like zonular ligaments ZL that extend generally radially outward to the ciliary muscle attachments. The lens capsule 102 has transparent flexible anterior and posterior walls or capsular membranes that contain the crystalline lens matrix LM.
Accommodation occurs when the ciliary muscle CM contracts to thereby release the resting zonular tension on the equatorial region of the lens capsule 102. The release of zonular tension allows the inherent elasticity of the lens capsule to alter it to a more globular or spherical shape, with increased surface curvatures of both the anterior and posterior lenticular surfaces. The lens capsule together with the crystalline lens matrix and its internal pressure provides the lens with a resilient shape that is more spherical in an untensioned state. Ultrasound biomicroscopic (UBM) images also show that the apex of the ciliary muscle moves anteriorly and inward—at the same time that the equatorial edge the lens capsule moves inwardly from the sclera during accommodation.
When the ciliary muscle is relaxed, the muscle in combination with the elasticity of the choroid and posterior zonular fibers moves the ciliary muscle into the unaccommodated configuration, which is posterior and radially outward from the accommodated configuration. The radial outward movement of the ciliary muscles creates zonular tension on the lens capsule to stretch the equatorial region of lens toward the sclera. The disaccommodation mechanism flattens the lens and reduces the lens curvature (both anterior and posterior). Such natural accommodative capability thus involves contraction and relaxation of the ciliary muscles by the brain to alter the shape of the lens to the appropriate refractive parameters for focusing the light rays entering the eye on the retina—to provide both near vision and distant vision.
In conventional cataract surgery as depicted in FIGS. 1B and 1C, the crystalline lens matrix is removed leaving intact only the thin walls of the anterior and posterior capsules—together with zonular ligament connections to the ciliary muscles. The crystalline lens core is removed by phacoemulsification through a curvilinear capsularrhexis as illustrated in FIG. 1B, i.e., the removal of an anterior portion of the capsular sac. FIG. 1B then depicts a conventional 3-piece IOL just after implantation in the capsular sac.
FIG. 1C next illustrates the capsular sac and the prior art 3-piece IOL after a healing period of a few days to weeks. It can be seen that the capsular sac effectively shrink-wraps around the IOL due to the capsularrhexis, the collapse of the walls of the sac and subsequent fibrosis. As can be easily understood from FIGS. 1B and 1C, cataract surgery as practiced today causes the irretrievable loss of most of the eye's natural structures that provide accommodation. The crystalline lens matrix is completely lost—and the integrity of the capsular sac is reduced by the capsularrhexis. The shrink-wrap of the capsular sac around the IOL damages the zonule complex, and thereafter it is believed that the ciliary muscles will atrophy.
Prior Art Pseudo-Accommodative Lens Devices.
At least one commercially available IOL, and others in clinical trials, are claimed to “accommodate” even though the capsular sac shrink-wraps around the IOL as shown in FIG. 1C. If any such prior art lens provide variable focusing power, it is better described as pseudo-accommodation since all the eye's natural accommodation mechanisms of changing the shape of the lens capsule are not functioning. Perhaps the most widely known of the pseudo-accommodative IOLs is a design patented by Cumming which is described in patent disclosures as having hinged haptics that are claimed to flex even after the capsular sac is shrink-wrapped around the haptics. Cumming's patents (e.g., U.S. Pat. Nos. 5,496,366; 5,674,282; 6,197,059; 6,322,589; 6,342,073; 6,387,126) describe the hinged haptics as allowing the lens element to be translated forward and backward in response to ciliary muscle contraction and relaxation within the shrink-wrapped capsule. The Cumming IOL design is being commercialized by C&C Vision, 6 Journey, Ste. 270, Aliso Viejo, Calif. 92656 as the CrystaLens AT-45. However, the medical monitor for the CrystaLens AT-45 in Phase I FDA trials explained in an American Society of Cataract and Refractive Surgeons (ASCRS) presentation, when asked about movement of AT-45's hinged haptics, that the AT-45 was not “moving much” at the optic and hinge. It is accepted that the movement of such a lens is entirely pseudoaccommodative and depends on vitreous displacement that pushes the entire IOL slightly anteriorly (see: http://www.candcvision.com/ASCRSCCTa-lks/Slade/Slade.htm). A similar IOL that is implanted in a shrink-wrapped capsule and in sold in Europe by HumanOptics, Spardorfer Strasse 150, 90154 Erlangen, Germany. The HumanOptics lens is the Akkommodative 1CU which is not available in the U.S., due to lack of FDA approval. In sum, any prior art IOLs that are implanted in an enucleated, shrink-wrapped lens capsule probably are not flexed by ciliary muscle relaxation, and exhibit only a pseudo-accommodative response due to vitreous displacement.
Since surgeons began using IOLs widely in the 1970's, IOL design and surgical techniques for IOL implantation have undergone a continuous evolution. While less invasive techniques for IOL implantation and new IOL materials technologies have evolved rapidly in the several years, there has been no real development of technologies for combining the capsular sac with biocompatible materials to provide a biomimetic capsular complex. What has stalled all innovations in designing a truly resilient (variable-focus) post-phaco lens capsule has been is the lack of sophisticated materials.
What has been needed are materials and intraocular devices that be introduced into an enucleated lens capsule with a 1 mm. to 2.5 mm. injector, wherein the deployed device and material provide the exact strain-absorbing properties and strain-releasing properties needed to cooperate with natural zonular tensioning forces. Such an intraocular device will allow for the design of dynamic IOLs that can replicate natural accommodation. Microdevices of intelligent elastic composite materials can provide the enabling technology to develop new classes of accommodating IOL systems.